1. Field of the Invention
The present invention relates generally to the field of energy harvesting. More specifically, the present invention relates to the field of electrical energy generation and includes, for example, methods, systems, and devices for converting flowing fluids into electrical power. Further, for example, the present invention relates to fluid-powered generators and methods, systems, and devices for generating electrical energy with such fluid-powered generators.
2. Description of Related Art
There exists a continued interest around the world in the development of alternative energy sources from sources that cannot be exhausted and/or are renewable. Harnessing and using local resources for energy has the advantage of potentially reducing dependence on foreign sources of energy, such as foreign oil, and contributing to local economy. Further, using resources, such as wind, and water, as energy sources to generate power, for example, electrical power, has obvious environmental advantages as well. Finding more efficient ways to use wind and water resources will benefit our society and environment on a global level.
Some considerations present in determining whether harnessing natural or manmade resources, such as wind and water resources, is an effective alternative to conventional coal, oil, and gas resources include assessing the associated financial and aesthetic costs. It is well known that one solution for producing more energy from wind or water power is to create larger devices for harnessing these resources. Larger devices, however, may lead to greater safety concerns, noise concerns, and can even be an aesthetic eyesore to some. Additionally, because devices for harnessing wind and water power are typically exposed to the elements, such devices are usually situated out in the open. As a result of using larger devices to harness these natural resources, more land is typically a prerequisite to installing them, which in turn increases acquisition and maintenance costs of real estate, for example. Additionally, portable devices for converting wind and/or water power could likewise be advantageous for their remote servicing capabilities especially in emergency situations.
Wind and water resources have advantages and disadvantages, which are primarily dependent on factors that may be difficult or improbable to control. For example, wind and water are unpredictable energy sources, which can vary with the weather, by geographic location, and from day to day. Even further, wind and water resources can be affected by a number of other considerations, including buildings, towers or other structures, trees, and terrain to name a few, which may interfere with the amount and/or intensity of these resources that can be harnessed and converted to electrical energy.
Providing a reasonably steady, continuous, and sufficient source of electrical energy from wind and/or water resources is a goal in making alternative energy sources more attractive. To date, however, this goal has not easily been achieved.
In particular, with respect to harnessing wind energy, it is well understood that the amount of electrical energy that can be generated from wind is dependent, at least in part, on the velocity and/or air mass density of the wind. Because wind velocity and air density can be at times unpredictable and/or fluctuating, it is difficult to achieve a reasonably steady, continuous, and sufficient output of electrical power from such systems. Thus, it would be advantageous to develop methods, devices, and systems for generating power that can operate over a wide range of wind or water conditions.
With respect to fluid-based power generators, in general, most power generating systems are not able to produce a useful amount of energy when the conditions presented by a particular fluid fluctuate greatly, e.g., drop below minimum required levels, or even exceed maximum allowed operating parameters for a particular generator. With respect to wind-based power generation, in particular, when the wind speed drops below a certain level, the generator may not operate or may not be able to produce a useful amount of energy. Most existing designs are not capable of operating below ambient wind speeds of, for example, 15 mph. Likewise, when the wind speed exceeds a level that can be tolerated by a generator, the generator will shut down as a result of or to prevent overheating. Most existing systems for fluid-based power generation are, thus, unreliable and/or impractical over a wide range of operating conditions.
There exists, therefore, a need for generators that can operate over a wide range of fluid velocities and that can provide a relatively constant power output, regardless of the conditions presented by the fluid. With respect to wind-based power generation, for example, it would be advantageous to develop devices that are capable of providing a reasonably steady, continuous, and sufficient source of electrical energy and at a fixed frequency of AC power so the transformers can be simplified, made cheaper and more reliable. For example, it is desirous to have a fluid-based turbine generator that is capable of providing a relatively consistent power output, regardless of whether the generator is operating at a low fluid speed, such as a wind speed of 3 mph, or at a high fluid speed, such as at hurricane-level wind speeds. There have been numerous attempts to provide energy generators to address at least some of these concerns but none have addressed all conditions (i.e., the low speed, high speed, and constant power).
For example, U.S. Pat. No. 4,720,640, entitled “Fluid Powered Electrical Generator,” describes an impellor-rotor mounted on a central support structure, with the outward ends of the blades of the fan being connected together by rotor rings. A peripheral electrical generator produces electrical energy when the impellor-rotor is driven by the fluid stream. Also provided is a downstream diffuser shroud to postpone, suppress, or eliminate what is referred to therein as a “stall” condition. The downstream diffuser shroud can be made of a flexible material for the purpose of flexing to conform to the changing conditions of the fluid on the output end of the system in response to an increase or decrease in fluid velocity through the diffuser shroud. FIG. 22 shows variability in the power output from the devices and, in particular, as wind velocity increases, the power density from the devices also increases, and FIG. 22 shows no appreciable power density for wind velocities below about 10 mph.
U.S. Pat. No. 4,075,500, entitled “Variable Stator, Diffuser Augmented Wind Turbine Electrical Generator System,” and incorporated herein by reference in its entirety, includes a mechanism for varying the effective angle of attack on the rotor with respect to the wind. The devices operate to provide the proper approach and pre-swirling of incoming wind by using stators with trailing edge flaps to rotate the rotor as desired.
U.S. Pat. No. 6,836,028, entitled “Segmented Arc Generator,” and incorporated herein by reference in its entirety, discloses converting mechanical power such as wind or water power into electrical power at a wide range of wind or shaft speeds. Devices described use a rotor ring that is in close proximity to a stator ring and some include a wind collector (for example, FIG. 4) to maximize exposure to wind. The wind collector is described as a funnel that increases the amount of air that is forced through the generator. The wind collector is fixed and can be rotated to an optimal position for receiving wind or to prevent damage in high wind conditions. Through use of a series stator coil connection by the switching matrix and voltage step-up by the boost converter, extraction of output power at 10% or less of rated speed can be achieved. The output power for continuous operation above rated speed is limited to the rated value due to current heating. Further, a power conditioning circuit enables the generator modules to operate efficiently at a wide range of fan speeds and a variable frequency control feature maintains constant voltage all through the designed RPM range.
U.S. Pat. No. 7,018,166, entitled “Ducted Wind Turbine,” and incorporated herein by reference in its entirety, describes devices with a duct having a convergent and a divergent surface to control the fluid flow pattern along the inner duct surface. In addition to a drive rotor, a free rotor is used to reduce the pressure of air immediately upstream of the free rotor to, in turn, increase the velocity of air at the throat of the duct and, thus, the speed of the drive rotor.
U.S. Pat. No. 6,939,101, entitled “Windmill,” and incorporated herein by reference in its entirety, provides devices for generating electricity, i.e., windmills having wind guide plates extending in a radial direction and an upper plate for preventing dispersion of the wind to collect the wind and thereby increase air density. Electricity can be stably generated using wind force irrespective of wind direction or wind velocity. The windmill can be installed in urban areas and mountain villages where wind direction and wind velocity frequently change.
“Flap-cone Control of Windmill Speed,” in Alternative energy sources; Proceedings of the Miami International Conference, Miami Beach, Fla., Dec. 5-7, 1977, Volume 4, Washington, D.C., Hemisphere Publishing Corp., 1978, pages 1681-1692, which is incorporated herein by reference in its entirety, discloses a flap-cone method of controlling windmill speed. FIG. 2 shows a fixed inlet, which captures one volume of air for the system. The speed of the air is controlled by adjusting the flap cone at an outlet portion of the cone.
Previous attempts to solve some of the problems associated with non-conventional energy generation systems have maintained a focus different from that of the present invention. By controlling turbine speed within an optimum range of operating speeds for a particular generator, the power output of such systems can likewise be controlled to maintain an optimum range of power output. Using fluids for power in such systems can complicate this goal, especially, as described above, when the fluid flow is affected by external factors that are difficult to control. As the inventor of the present invention has discovered, turbine speed can be controlled with the inventive inlets described below, which control the amount of fluid collected by an energy generator system, regardless of the conditions presented by external fluid flow.
As contrasted with the above-described energy generating systems, the inventive methods, systems, and devices for energy generation are capable of operating over a wide range of fluid speeds, while providing a reasonably steady, continuous, and sufficient source of electrical energy by having inlet means for controlling fluid flow and turbine speed of fluid-powered turbine generators.